Field of the Invention
The present invention relates to an image forming apparatus using an electrophotographic method.
Description of the Related Art
In recent years, in an image forming apparatus in which a color image is formed on a recording material by using an electrophotographic method, such as a color laser printer, color gamut has become important as one of high image quality indexes of the output image. The color gamut represents a color reproduction range that can be reproduced by the image forming apparatus, and a wider color gamut corresponds to a wider color reproduction range. As a method of enlarging the color gamut, for example, in a color image forming apparatus, dense Y, dense M, and dense C developers are used in addition to developers of four colors Y, M, C and K that are usually used, and a wide color gamut is realized by using developers with more than four colors.
As another method, it is conceivable to increase the color gamut of the output image fixed to the recording material to above the usual level by increasing the amount of developer (referred to hereinbelow as “toner amount”) placed on the recording material to above the usual level. Further, as a method for changing the toner amount, it is conceivable to change the peripheral velocity ratio of a photosensitive drum as an image bearing member and a developing roller as a developer bearing member. As a method for changing the peripheral velocity ratio of the photosensitive drum and the developing roller, Japanese Patent Application Publication No. H8-227222 suggests a method for adjusting the tinge of the secondary color (red color) by changing the rotation speed of the developing roller. Further, Japanese Patent Application Publication No. 2013-210489 suggests a method for improving image graininess, that is, reducing toner scattering and image blurring, by reducing the rotation speed of the photosensitive drum.